This project is designed to investigate the roles of two related members of the mitogen-activated protein kinase (MAPK) family, i.e., extracellular signal-regulated kinase (ERK) and p38 MAPK in the development and differentiation of oligodendrocytes, the key cells of myelination and demyelination in the CNS. The studies have implications for an understanding of the molecular mechanisms of neural development, myelination and remyelination in demyelinating diseases such as multiple sclerosis. Since the development of oligodendrocytes is stringently controlled by environmental signals, the long-range objective of this research will define signal transduction mechanisms regulating their differentiation and the expression of myelin-specific genes. Primary cultures of rat brain oligodendrocyte progenitors responding to growth/differentiation stimuli will serve as the experimental model to accomplish the following specific aims: * Specific inhibitors of ERK and p38 MAPK will be used to investigate the roles of the two kinases in mitogenic induction and lineage progression (i.e., expression of stage-specific antigens) of oligodendrocyte progenitors as well as in the reciprocal regulation of the levels of key cell cycle regulators, i.e., cyclin D1 (an activator of cyclin-dependent protein kinase, cdk) and p27 (a cdk inhibitor). * The roles of p38 MAPK isoforms and ERKs in oligodendrocyte differentiation will be further characterized using a molecular approach, i.e., transfection with dominant negative and/or constitutively active forms of p38 MAPK isoforms (i.e., alpha and beta) and ERKs (i.e., ERKI and ERK2) as well as their upstream kinases followed by an analysis of the expression of differentiation markers. Putative cytoplastic and nuclear targets (i.e., CREB, ATF2, C/EBP and MEF2C) of p38 MAPK pathway that may signal oligodendrocyte differentiation will be characterized. * p38 MAPK-mediated transcriptional activation of oligodendrocyte-specific genes (i.e., myelin basic protein, protoelipid protein) will be examined using promoter-reporter constructs co-transfected with constitutively active forms of the kinases. Putative MAPK-responsive elements and relevant binding activities will be determined by deletion and gel shift analyses